Field of the Invention
Exemplary embodiments of the present invention relate to a method of manufacturing tailor welded blanks manufactured by interconnecting steel plates having different thicknesses and materials, and more particularly, to a method of manufacturing tailor welded blanks, capable of improving a quality of a welded portion and shortening a manufacturing time when a tailor welded blank is manufactured using a coated steel plate.
Description of Related Art
In recent years, requirements to vehicles for reinforcement of environments and safety regulations have been continually strengthened. That is, in order to correspond to a lightening demand for improvement in fuel efficiency and enhancement of collision safety, high strength steel including AHSS (Advance High Strength Steel), for example, tends to be widely applied to vehicles.
High strength parts are applied during manufacturing of a vehicle body to cope with a side collision. Particularly, the role of side pillars is very important for protection of a battery during a side collision in an electric vehicle, compared to that of the vehicle body in an existing internal combustion engine. To this end, super high strength steel by an HPF (Hot Press Forming) technique is increasingly used.
Meanwhile, collision absorption parts may be largely classified into two parts.
One is an energy absorption part which absorbs impacts applied from the outside through deformation thereof.
The energy absorption part is representatively applied to each of the front of a front side member, the rear of a rear side member, and the bottom of a B-pillar.
The other is an anti-intrusion part which is not nearly deformed. For example, since a cabin zone occupied by occupants should be secured during a collision, the collision absorption part applied to the cabin zone is mostly the anti-intrusion part.
The anti-intrusion part is representatively applied to each of the rear of the front side member, the front of the rear side member, and the top of the B-pillar.
The use of the anti-intrusion part to which the HPF technique is applied is rapidly increased to improve collision safety. The AHHS having a relatively high strain rate is applied to the energy absorption part.
The combined form of the energy absorption part and the anti-intrusion part is used in each of the front side member, the rear side member, and the B-pillar, and is manufactured by welding and forming the two parts.
In this case, a mainly used TWB (Tailor Welded Blank) method includes a series of processes of manufacturing parts by cutting steel plates having different thicknesses, strengths, and materials to a required shape as if cutting out a suit, welding and the cut steel plates, and then forming the welded steel plates with a press. The TWB method is largely configured of a cutting process of cutting steel plates, a welding process of welding the cut steel plates with laser, and a blanking process of integrally machining the welded steel plates.
Since different steel plates having different thicknesses and materials are welded by the TWB method, the welded part may have characteristics required for each portion. In addition, the different steel plates may be manufactured to have an accurate dimension as well as a strong structure and a long life by the TWB method, compared to a single steel plate. Therefore, the TWB method is applied during production of structures such as body panels of vehicles or electric rail vehicles.
Particularly, the TWB method may achieve reduction of the number of parts, vehicle body lightening, manufacturing cost reduction, quality improvement, collision safety improvement, vehicle body structure simplification, and the like, compared to a conventional forming method of manufacturing parts by cutting steel plates, forming each of the cut steel plates, and then spot-welding the formed steel plate during production of structures such as vehicle body panels, in vehicle industrial fields requiring high productivity, low cost, and low weight.
However, in a coated steel plate having an Al—Si or Zn coated layer, it is difficult to secure an austenite structure even when the coated steel plate is heated at a temperature of 900 to 950° C. and it is difficult to secure a martensite structure ever when the coated steel plate is quenched, since the coated layer is mixed into a welded portion during laser welding. For this reason, there is a problem in that material properties of the welded portion are deteriorated.
Accordingly, it is necessary to remove the coated layer from the coated steel plate in order to weld the coated steel plate. However, there is a problem in that a quality of the production part is deteriorated since rust is generated at a removed portion of the coated layer for welding.